Oxidation resistant material



3,291,577 OXIDATION RESTSTANT MATERIAL Gail F. Davies, Mentor Township, and Raymond H.

Baskey, Cleveland, Ohio, assignors to Clevite Corporation, a corporation of Ohio No Drawing. Filed Sept. 12, 1963, Ser. No. 308,354 9 Claims. (Cl. 29-1822) This invention generally relates to an oxidation resistant material and, more particularly, to a nickel-chrome base material having a high strength to weight ratio at temperatures of 2000 F. and above.

'Materi'als currently available to perform satisfactorily at elevated temperatures and at a high load, are primarily refractory metals. These metals have a very high melting point, however, one of their characteristics is a very poor oxidation resistance at high temperatures. Illustrative of this type of performance are materials such as tungsten or molybdenum which will perform well in a reducing atmosphere, but are short lived at a temperature of 2000 F. under oxidizing conditions. On the other hand, high oxidation resistant materials singularly lack the strength of the. refractory materials at elevated temperatures.

In accordance with this invention, these disadvantages are overcome by providing an oxidation resistant material exhibiting a high strength to weight ratio at elevated temperatures. The material is composed of a powder metal matrix of predominantly nickel and chrome particles. A plurality of fibers, selected from a group of refractory metals, e.g., tungsten, molybdenum, tantalum and niobium and alloys thereof, are dispersed through the matrix and are individually bonded thereto.

These preferred characteristics are exhibited at elevated temperatures and disappear gradually towards lower temperatures, and are non-existent at room temperatures where the matrix strength exceeds the strength of the reinforcing media. It is believed that the lack of strengthening at the lower range of temperatures is due to a number of reasons. One may be the embrittling of the fibers. Another reason may be related to the embrittling of the diffusion zone formed between the fibers and the matrix. In any event, the properties at elevated temperatures are very materially enhanced as can be seen from Table No. I.

TABLE I Hot Pressed Hot Pressed N iCr With N iCr 21.7 V/O Tungsten Wires Density, #/in. O. 301 0. 386 Melting Point, F 2, 550 Tensile Strength at Room Temp. (p.s.i.).. 107, 000 73, 000 Tensile Strength at 2,000 F. (p.s.i) 7, 900 47, 600 Tensile Strength/Density Ratio at Room Temperature (iuchesXw 3. 57 1. 89 Tensile Strength/Density Ratio at 2,000

F. (ineheSXlO 0. 27 1.23

As can be gleaned from Table No. I, applicants have provided an oxidation resistant material which has a hot strength approximately eight times greater than nickel chrome materials of a conventional nature.

It is therefore the primary object of our invention to providea high-strength oxidation-resistant composite product, combining these preferred properties and including the property to perform satisfactorily in oxidizing conditions at a temperature of at least 2200 F. Such material has broad application as a structural material, or in sheet form, and can be used for the manufacture of metallurgical furnace trays or accessory materials such as, for instance, no-sag. furnace ribbons, wires, or tubing.

1. Another object of this invention is to further enhance the versatility of subject material by providing an overlay 3,291,577 Patented Dec. 13, 1966 composition range suitable for the manufacture of subject invention is approximately: 7

Nickelfrom about 70 to about 90 weight percent Chrome-from about 10 to about 30 weight percent.

A preferred mixture has the following composition:

Nickel-about weight percent Chrome-about 20 weight percent.

The nickel chrome matrix is fiber reinforced to improve the hot strength of the composite. The fibers may be either continuous or discontinuous. The length of discontinuous fibers is from about to about 3", while the continuous fibers have a length substantially equivalent to the length of the composite. The preferred diameter of the continuous as well as the discontinuous fibers is from about 0.001" to about 0.050. The fibers are selected from a group of refractory metals consisting of tungsten, molybdenum, tantalum, and niobium, or alloys thereof in which the refractory materials predominate. The fiber content of the composite structure is about 5 to 40% of the volume of the composite. While there are numerous variables entering into the determination of the fiber volume content such as, the length and diameter of the fibers and the degree of alignment in the composition, it appears that a fiber volume content of about 20%, on the average, brings best results.

Depending upon the oxidizing conditions to which the composite is to be exposed, and the fabricability required in the final application, it is at times desirable to provide a thin overlay surrounding the composite structure. This overlay varies somewhat in its thickness, however, a layer of 0.001 to 0.005" thick has been found to be very satisfactory. In accordance with this invention this overlay is composed of a nickel and chrome composition which is similar to the nickel-chrome composition of the matrix material described above.

A typical example of a process schedule used to produce the oxide resistant material in accordance with this invention, is as follows:

A suitable percentage of nickel chrome powder particles are selected, as well as a suitable quality and quantity of reinforcing fibers. The fibers are cut if necessary to a predetermined length.

The fiber materials are then cleaned to enable an optimum bond with the powder particles.

The composite mixture of the powder particles and the metallic fibers are then blended, and are charged as uniformly mixed into a compression die. In the case of cold pressing, the material in the die is subjected to pressures of 50 to 60 p.s.i. A thin layer of overlay material is then placed along the bottom of an oversized die, the compacted matrix is placed into the die and a layer of overlay material is placed on top and along the side of the precompacted piece. Then the composite as a whole is pressed once more and thereafter suitably sintered in a reducing atmosphere at a temperature not in excess of 2300 F. Preferably, for cold pressing, the time should not exceed one hr./in.

As has already been noted above, the fibers can either be dispersed in the matrix at random or aligned in the matrix with a specific orientation. It has been found that maximum strength occurs along the axis of alignment of the majority of fibers. Such alignment of the fibers can be obtained by various mechanical means which are well known to those versed in the art. Although the discontinuous or continuous fibers are aligned in one direction, it is, nevertheless, important to observe that the fibers are evenly spaced throughout the matrix body in order to obtain a homogenous sheet material. If such requirement is not met and they are dispersed without any degree of uniformity, the composite will generally crack during the rolling process.

The Tables 11 and III show certain variables effecting composite structures containing randomly and aligned fibers and indicate some optimum characteristics.

4. An oxidation resistant material having a high strength to Weight ratio at elevated temperatures comprising: a powder metal matrix consisting essentially of about 80 weight percent nickel and about 20 weight percent chrome, and a plurality of fibers selected from a group of refractory metals consisting of tungsten, molybdenum, tantalum, and dispersed substantially evenly throughout said matrix and bonded thereto without being mechanically interlocked relative to each other, said fibers constituting about 5 to about 40 percent of the volume of the structure.

5. An oxidation resistant material having a high strength to weight ratio at elevated temperatures comprising: a powder metal matrix consisting essentially of about 80 weight percent nickel and about 20 weight percent TAB LE II.RAND OM DIST RIB UTION Vol. Percent Fibers 5 1 mil 1 mil Diameter 2 mil 2 mil 3 mil 3 mil-.- Length 34" orless or 1e Diameter 5 mil 5 mil.-. i1 m1 1 m1 rm Length to V... to to 3 or less..- $4," or less..- or less..- M or less..- 3 or less. Diameter 10 mil to 20 10 mil to 20 10 mil to 20 10 mil to 20 10 mil to 20 10 mil to 20 10 mil to 20 10 mil to 20 mil. rru'l. mil. mil. m mil. mil. mil. Length Me" to y"-- M to M,.. A6 to a. lie to or less... or less... or less... or less.

TABLE IIL-ALIGNED PATTERN Vol. Percent Fibers 5 10 15 2O 25 30 35 40 Diameter 1 to 5 mil.- 1 to 5 mil... 1 to 5 mil.... 1 to 5 mil.... 5 rml mil 5 mil. Length M6 to full 546 to full A5 to full M6" to full M6" to full Me to full A5 to full ie" to full length. length. length. length. length. length. length. length. Diameter.. 5 to 10 mil... 5 to 10 mil... 5 to 10 mil 5 to 10 mil 5 to 10 m1l... 5 to 10 mil... 5 to 10 mil... 5 to 10 mil. Length M0 to lull Mo" to full Me" to full Me" to full /lfi to full M6 to full lie" to full 540 to full length. length. length. length. length. length. length. length.

Powder metallurgical methods other than those mentioned above can be used with equal facility, although the tensile strength to weight ratio may differ from method to method.

While there have been described what are at present considered to be the preferred embodiments of this invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is aimed, therefore, in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. An oxidation resistant material having a high strength to weight ratio at elevated temperatures comprising: a powder metal matrix consisting essentially of nickel and chrome particles; and a plurality of fibers selected from a group of refractory metals consisting of tungsten, molybdenum, tantalum and niobium and alloys thereof dispersed substantially evenly throughout said matrix and bonded thereto without being mechanically interlocked relative to each other and having a diameter less than about 0.020 inch and a length of not substantially less than 0.0675 inch.

2. An oxidation resistant material having a high strength to weight ratio at elevated temperatures comprising: a powder metal matrix consisting essentially of about 70 to 90 weight percent nickel and about 10 to 30 weight percent chrome; and a plurality of fibers selected from a group of refractory metals consisting of tungsten, molybdenum, tantalum and alloys thereof dispersed substantially evenly throughout said matrix and bonded thereto without being mechanically interlocked relative to each other.

3. An oxidation resistant material according to claim 2, wherein said refractory fibers constitute about 5 to about 40 percent of the volume of the structure.

chrome, and a plurality of tungsten fibers dispersed substantially evenly throughout said matrix and bonded thereto without being mechanically interlocked relative to each other, said fibers constituting about 20 percent of the volume of the structure.

6. An oxidation resistant material having a high strength to weight ratio at elevated temperatures comprising: a powder metal matrix consisting essentially of nickel and chrome particles; and a plurality of fibers selected from a group of refractory metals consisting of tungsten, molybdenum, tantalum and dispersed substantially evenly throughout said matrix and bonded thereto without being mechanically interlocked relative to each other, and a metallic overlay predominantly composed of about 70 to weight percent nickel and about 10 to 30 volume percent chrome particles encapsulating the said matrix.

7. A material according to claim 6, wherein said overlay has a thickness in the range of about .001 inch to about .005 inch.

8. An oxidation resistant material having a high strength to weight ratio at elevated temperatures comprising: a powder metal matrix consisting essentially of about 70 to 90 weight percent nickel and about 10 to 30 weight percent chrome; and a plurality of fibers selected from a group of refractory metals consisting of tungsten, molybdenum, tantalum and dispersed substantially evenly throughout said matrix and bonded thereto without being mechanically interlocked relative to each other, and a metallic overlay predominantly composed of about 70 to 90 weight percent nickel and about 10 to 30 weight percent chrome particles encapsulating the fiber reinforced matrix.

9. An oxidation resistant material having a high strength to weight ratio at elevated temperatures comprising: a powder metal matrix consisting essentially of about 70 to 90 weight percent nickel and about 10 to 30 weight percent chrome; and a plurality of tungsten fibers dispersed UNITED References Cited by the Examiner STATES PATENTS Lorenz.

Ransley et a1. 29--191.2 Goetzel 75208 X Conant 75208 X 6 3/1963 Whittemore 75-208 X 4/1963 McDaniels et a1. 12/1963 Du Bois et al. 29182.2 12/1964 Black et al. 75-208 X 5/1965 Becker et a1. 29182.3 X

FOREIGN PATENTS 3/1954 Great Britain.

10 L. DEWAYNE RUTLEDGE, Primaly Examiner.

CARL D. QUARFORTH, LEON D. ROSDOL,

Examiners.

R. L. GRUDZIECKI, Assistant Examiner. 

1. AN OXIDATION RESISTANT MATERIAL HAVING A HIGH STRENGTH TO WEIGHT RATIO AT ELEVATED TEMPERATURES COMPRISING: A POWER METAL MATRIX CONSISTING ESSENTIALLY OF NICKEL AND CHROME PARTICLES; AND A PLURALITY OF FIBERS SELECTED FROM A GROUP OF REFRACTORY METALS CONSISTING OF TUNGSTEN, MOLYBDENUM, TANTALUM AND NIOBIUM AND ALLOYS THEREOF DISPERSED SUBSTANTIALLY EVENLY THROUGHOUT SAID MATRIX AND BONDED THERETO WITHOUT BEING MECHANICALLY INTERLOCKED RELATIVE TO EACH OTHER AND HAVING A DIAMETER LESS THAN ABOUT 0.020 INCH AND A LENGTH OF NOT SUBSTANTIALLY LESS THAN 0.0675 INCH. 